Having previously determined that the initial reaction sequence in exercise-induced asthma has to do with heat loss from the respiratory tract and airway cooling, we spent this year investigating whether this stimulus activates mast cells within the tracheobronchial tree, and how various agents affect the response. In addition, we studied the airway effects of respiratory heat loss in non-asthmatic subjects. From these efforts, we have learned that mediators of immediate sensitivity do not appear to play a role in this condition and that drugs such as atropine can interact with the stimulus. Further, we now can make normal people respond to airway cooling.